1. Field of the Invention
The present invention relates to a circuit substrate and a method of manufacturing the same. More specifically, the present invention relates to a circuit substrate having a structure which enables conduction between the two sides of a substrate via a conductor in a through hole provided in the substrate, and relates to a method of manufacturing the same.
2. Description of the Related Art
Heretofore, there are circuit substrates having a structure in which wiring layers formed on both sides of a silicon substrate are connected to each other through conductors provided in through holes of the silicon substrate.
A method of manufacturing such a circuit substrate will be described. As shown in FIG. 1, first, through holes 100x are formed in a silicon substrate 100, and then the silicon substrate 100 is thermally oxidized, whereby a first insulating layer 110 is formed on both surfaces of the silicon substrate 100 and the inner surfaces of the through holes 100x. Subsequently, wiring layers 130 connected to each other via through electrodes 120 in the through holes 100x are formed on both sides of the silicon substrate 100 by a semi-additive process or the like. Moreover, a second insulating layer 140 having opening portions 140a provided on pad portions of the wiring layer 130 is formed on each side of the silicon substrate 100. A thing similar to this circuit substrate is described in Patent Literature 1 (Japanese Unexamined Patent Publication No. 2004-311574).
Moreover, there is a circuit substrate in which conduction between the two sides of a substrate is made possible by inserting conductive components into through holes provided in the substrate. It is described in Patent literature 2 (Japanese Unexamined Patent Publication No. 2001-352166) that a coaxial line structure which enables conduction between the two sides of a core substrate is formed by forming a conductor layer on the inner walls of through holes of the core substrate and then inserting through hole components having a structure in which a core wire is covered with resin into the through holes.
Furthermore, it is described in Patent Literature 3 (Japanese Unexamined Patent Publication No. Hei 5-183019) that a semiconductor device having a structure in which conductive pins are inserted in through holes of a semiconductor substrate, and upper portions of the conductive pins are connected to wiring on the upper side of the semiconductor substrate, and lower portions of the conductive pins are used as external connection terminals.
Furthermore, it is described in Patent Literature 4 (U.S. Pat. No. 6,717,071 B2) that a coaxial via hole structure in which outer and inner cylindrical conductors and an insulator filling the space in between are formed in a through hole of a substrate.
In recent years, there has been a demand for a wiring substrate having a structure in which two conducting paths electrically insulated from each other are formed in a through hole of a substrate, and one conducting path is connected to a first wiring layer on the substrate, and the other conducting path is connected to a second wiring layer on the substrate.
However, in the prior art, since one conducting path is formed in a through hole of a substrate, the number of through holes becomes large in the case where both sides of the substrate are connected to each other by two independent conducting paths. Thus, there is a problem that a wiring layout is limited.
Also, in Patent Literature 2 (Japanese Unexamined Patent Publication No. 2001-352166), two independent conducting paths can be formed in a through hole of a resin substrate. However, since this is a method in which conductive components are inserted into a through hole, it is very difficult to apply this method to fine through holes provided in a semiconductor substrate having a reduced thickness.
On the other hand, in Patent Literature 4 (U.S. Pat. No. 6,717,071 B2), a method is disclosed in which a coaxial capacitor or the like is formed in a through hole of a substrate, but no consideration is given to enabling conduction between the two sides of the substrate.